Still King: Why Kong Dwarfs Today's Beasts

King Kong is back, and bigger than ever, in the new movie "Kong: Skull Island" (Warner Bros. Pictures, 2017).

Credit: Warner Bros. Pictures

King Kong is back.

The famed film ape stomped back into theaters Friday (March 10) in the movie "Kong: Skull Island." The film explores the massive beast's origin story on the uncharted and mysterious island that he inhabits, along with a variety of other oversize and dangerous creatures.

Some land animals were once as large as Kong, or even bigger, but they are long extinct. And many animals alive today, such as wolves, bears, big cats and even primates, are significantly smaller than their extinct relatives that lived long ago. What enables animals to reach spectacular sizes, and why can't today's creatures achieve Kong-like stature?

Blue whales are the only modern animals that come close to matching Kong's great size, with adult whales measuring up to 100 feet (31 meters) long. But millions of years ago, creatures that were even larger walked the Earth — such as the dinosaur called Argentinosaurus, which measured about 140 feet (46.7 m) from nose to tail tip. The Argentinosaurus belonged to a dinosaur group known as sauropods, long-necked plant-eaters that lived 136 million to 66 million years ago and that represent the biggest land animals that ever lived.

Though Kong appears to be the last of his kind, enormous ape-like skulls and skeletons hint that other giant primates once roamed Skull Island.

Credit: Warner Bros. Pictures

Land mammals, however, have never quite managed to get as big as dinosaurs did. The largest land mammal of all time — a rhino-like herbivore called Indricotherium that lived between 34 million and 23 million years ago — stood only about 16 feet (5 m) tall. The biggest known primate — the hulking Gigantopithecus, which went extinct 100,000 years ago — barely cleared 10 feet (3 m) in height.

Different metabolic strategies could explain why mammals lagged where dinosaurs enlarged, said John Flynn, Frick Curator of Fossil Mammals in the Division of Paleontology at the American Museum of Natural History in New York City. [In Images: How King Kong Measures Up]

"Because they're warm-blooded, mammals have very high energetic needs," Flynn told Live Science. And the bigger the animal, the more costly it becomes to fuel that warm-blooded engine, he said.

"When you get to be [the] size of an elephant or an Indricotherium, you must find mechanisms to be incredibly efficient for extracting energy from the food that you get. Or you have to eat incredibly high-energy food, or you have to be eating all the time — or both," he said.

The island rule

The long and short of it is that a number of ecological factors help determine whether a species follows an evolutionary path to enormous size, said Mark Lomolino, a professor at the State University of New York College of Environmental Science and Forestry, and author of a study on the body-size evolution of island vertebrates, published in 2005 in the Journal of Biogeography.

"Body size determines how much you need to eat and how you can dominate other species in competition for resources. In mainland systems, species increase or decrease in body size to fill different niches," Lomolino told Live Science.

But on islands, the rules are different. There are usually fewer mammals than on the mainland, and that removes some of the forces that drive species to diversify, he said. However, a pattern called "the island rule" also emerges: Big animals tend to get smaller, and small animals tend to get bigger, Lomolino said. [The World's Biggest Beasts: Here and Gone (Photos)]

Animals on the fictional Skull Island, however, apparently ignored the island rule, as a primate that closely resembles a gorilla somehow evolved to be 100 feet tall.

Farewell to the giants

Many large mammals that are alive today have extinct relatives that were supersized — though not quite Kong size.

In the Northern Hemisphere during the last ice age, large mammal species like mastodons, mammoths, dire wolves, giant bears and saber-toothed cats all grew to be larger than their modern cousins. Many of those ancient beasts disappeared during what is known as the Quaternary extinction event, which occurred about 12,000 years ago, at the end of the Pleistocene epoch.

"They couldn't handle the new predator turning up," study lead author Chris Sandom, a lecturer in biology at the University of Sussex in the United Kingdom, told Live Science in 2014.

And in a world increasingly shaped by human activity, the biggest wild animals alive today face an uncertain future. In fact, most of Earth's largest creatures — about 59 percent of carnivores and 60 percent of herbivores — could be extinct by 2100, conservation biologists warned in a study published in July 2016 in the journal BioScience.

The researchers outlined steps that could halt or slow destructive practices threatening big animals, such as rhinos, gorillas and tigers. But unless action is taken — and quickly — the planet could face a future in which any kind of large wildlife seems as fantastic as the great beast King Kong, and can only be glimpsed in movies.

Mindy Weisberger is a senior writer for Live Science covering general science topics, especially those relating to brains, bodies, and behaviors in humans and other animals — living and extinct. Mindy studied filmmaking at Columbia University; her videos about dinosaurs, biodiversity, human origins, evolution, and astrophysics appear in the American Museum of Natural History, on YouTube, and in museums and science centers worldwide. Follow Mindy on Twitter.